.\"	$OpenBSD: getpriority.2,v 1.14 2013/07/17 05:42:11 schwarze Exp $
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.\"     @(#)getpriority.2	8.1 (Berkeley) 6/4/93
.\"
.Dd $Mdocdate: July 17 2013 $
.Dt GETPRIORITY 2
.Os
.Sh NAME
.Nm getpriority ,
.Nm setpriority
.Nd get/set process scheduling priority
.Sh SYNOPSIS
.Fd #include <sys/resource.h>
.Ft int
.Fn getpriority "int which" "id_t who"
.Ft int
.Fn setpriority "int which" "id_t who" "int prio"
.Sh DESCRIPTION
The scheduling priority of the process, process group, or user,
as indicated by
.Fa which
and
.Fa who
is obtained with the
.Fn getpriority
call and set with the
.Fn setpriority
call.
.Fa which
is one of
.Dv PRIO_PROCESS ,
.Dv PRIO_PGRP ,
or
.Dv PRIO_USER ,
and
.Fa who
is interpreted relative to
.Fa which
(a process identifier for
.Dv PRIO_PROCESS ,
process group identifier for
.Dv PRIO_PGRP ,
and a user ID for
.Dv PRIO_USER ) .
A zero value of
.Fa who
denotes the current process, process group, or user.
.Fa prio
is a value in the range \-20 to 20.
The default priority is 0; lower priorities cause more favorable scheduling.
.Pp
The
.Fn getpriority
call returns the highest priority (lowest numerical value)
enjoyed by any of the specified processes.
The
.Fn setpriority
call sets the priorities of all of the specified processes
to the specified value.
Priority values outside the range \-20 to 20 are truncated to the
appropriate limit.
Only the superuser may lower priorities.
.Sh RETURN VALUES
Since
.Fn getpriority
can legitimately return the value \-1, it is necessary
to clear the external variable
.Va errno
prior to the
call, then check it afterward to determine
if a \-1 is an error or a legitimate value.
The
.Fn setpriority
call returns 0 if there is no error, or
\-1 if there is.
.Sh ERRORS
.Fn getpriority
and
.Fn setpriority
will fail if:
.Bl -tag -width Er
.It Bq Er ESRCH
No process was located using the
.Fa which
and
.Fa who
values specified.
.It Bq Er EINVAL
.Fa which
was not one of
.Dv PRIO_PROCESS ,
.Dv PRIO_PGRP ,
or
.Dv PRIO_USER .
.El
.Pp
In addition,
.Fn setpriority
will fail if:
.Bl -tag -width Er
.It Bq Er EPERM
A process was located, but neither its effective nor real user
ID matched the effective user ID of the caller.
.It Bq Er EACCES
A non-superuser attempted to lower a process priority.
.El
.Sh SEE ALSO
.Xr nice 1 ,
.Xr fork 2 ,
.Xr renice 8
.Sh STANDARDS
The
.Fn getpriority
and
.Fn setpriority
functions conform to
.St -p1003.1-2008 .
.Sh HISTORY
The predecessor of these functions, the former
.Fn nice
system call, appeared in
.At v3
and was removed in
.Bx 4.3 Reno .
The
.Fn getpriority
and
.Fn setpriority
system calls appeared in
.Bx 4.1c .
